Already known, in particular from French patent application 2 834 662 to which corresponds the U.S. patent application 2005/0101235, from French patent application 2 857 610 to which corresponds to the U.S. patent application 2006/0154581 and from French patent application 2 900 356 to which corresponds the U.S. patent 2008/0171502, is a tool for surfacing an optical surface, comprising: a rigid support having a transverse end surface; an elastically compressible interface connected to the rigid support, comprising a part referred to as central which is located in line with said end surface of the rigid support and a part referred to as peripheral which is located transversely beyond said end surface of the rigid support; a flexible buffer adapted to be applied against a surface to work, connected to the interface on the opposite side to the rigid support, comprising a part referred to as central which is located in line with said end surface of the rigid support and a part referred to as peripheral which is located transversely beyond said end surface of the rigid support; as well as elastic return means disposed between said rigid support and the peripheral part of said interface, the combination of said peripheral part of the buffer, of said peripheral part of the interface and of the elastic return means forming a means for stabilizing the tool during the surfacing, said tool being adapted to perform surfacing for the most part at the central part of the buffer.
To reduce the roughness of the optical surface, the tool is brought into contact therewith by maintaining a sufficient tool pressure thereon for the buffer to conform to the optical surface, by deformation of the interface.
While irrigating the optical surface with a fluid, it is rotationally driven relative to the tool or (vice-versa) and is swept using that tool.
Generally, the optical surface is rotationally driven, its rubbing against the tool being sufficient to rotationally drive the tool conjointly.
The surfacing step requires an abrasive which may be contained in the buffer or in the fluid.
During the surfacing, the elastically compressible interface makes it possible to compensate for the difference in curvature between the end surface of the support for the tool and the optical surface.
An example embodiment of the tool proposed by French patent application 2 834 662, to which corresponds U.S. patent application 2005/0101235, is described below with reference to FIGS. 1 to 3 of the accompanying drawings, in which                FIG. 1 is an exploded perspective view of that tool and an ophthalmic lens having an optical surface to be surfaced;        FIG. 2 is a cross-section view of that tool when assembled, during the surfacing of the optical surface of the lens of FIG. 1; and        FIG. 3 is a diagrammatic view from above representing that ophthalmic lens during surfacing using that tool, which tool is represented during the sweeping of the optical surface in two positions one of which is illustrated in dashed line.        
In FIG. 1 there is represented a tool 1 for the surfacing of an optical surface 2, in this case one of the faces of an ophthalmic lens 3. In FIG. 1, as in FIG. 2, the optical surface 2 concerned is represented as being concave, but it could equally well be convex.
The tool 1 is formed by the stacking of at least three parts, i.e. a rigid part 4, an elastically compressible part 5, and a flexible part 6, which, in what is to follow, will respectively be called support, interface and buffer.
As can be seen in particular in FIG. 1, the support 4 comprises two jaws, i.e. a lower jaw 7 and an upper jaw 8 which are adapted to be superposed while fitting into each other via a pin 9 projecting from one face 10 of the faces of the upper jaw 8 and adapted to be received in a complementary hole 11 formed, facing it, in a face 12 of the lower jaw 7.
As may be seen in FIG. 1, the support 4 is of cylindrical general shape with rotational symmetry and has an axis of symmetry denoted X, which defines direction referred to as longitudinal.
The normal to the optical surface 2 at the point of intersection of the axis of symmetry X of the tool 1 with the latter is denoted n.
The lower jaw 7 has, remote from its face 12 in which the hole 11 is made, a substantially transversely extending end surface 13, against which is applied the interface 5, covering it.
The buffer 6 is applied against the interface 5 from the other side thereof relative to the support 4.
To be more precise, the buffer 6 at least in part covers the interface 5 on the opposite side to and in line with the end surface 13.
The rubbing of the buffer 6 against the optical surface 2 will, by means of an abrasive contained in the irrigating fluid or incorporated in the buffer 6 itself, provide superficial removal of material from the optical surface 2 for modification of the surface state, as will be seen below.
The buffer comprises a central part 6a which is located in line with the end surface 13, and comprises a peripheral part 14 which is located transversely beyond the end surface 13.
This peripheral part 14 is connected to the support 4 via elastic return means 15.
The peripheral part 14 extends in continuity with the central part 6a while being, at rest, substantially coplanar therewith.
In the example illustrated in FIGS. 1 and 2, the buffer 6 is in one piece, the peripheral part 14 being connected to the central part 6a such that they in fact form a single component.
In an embodiment represented in thick line in FIG. 1, the buffer 6 has the form of a flower, and thus comprises a plurality of petals 14b which, projecting transversely from the central part 6a, form the peripheral part 14 of the buffer 6 and which each extends transversely beyond the end surface 13.
In a variant represented in chain line in FIG. 1, the peripheral part 14 takes the form of a crown 14a which surrounds the central part 6a 
In this case, in the absence of stress, and when it is in one piece, the buffer 6 takes the form of a disk of material of small thickness compared with its diameter, as represented in FIG. 1, the peripheral part 14, 14a thereby forming a collar with respect to the end surface 13.
The return means 15, which will be described later, may be directly interposed between the support 4 and the peripheral part 14 of the buffer 6, that is to say, in practice, the collar 14a or the petals 14b 
The interface 5 comprises not only a central part 5a which is located in line with the end surface 13, but also a peripheral part 16 which is located transversely beyond the end surface 13.
This peripheral part 16 follows on from the central part 5a, and, for example, in the absence of stress, takes the form of a crown which surrounds the central part 5a, and which is in fact interposed between the peripheral part 14 of the buffer 6 and the return means 15.
As can be seen in FIGS. 1 and 2, the interface 5 is in one piece, its central part 5a and peripheral part 16 in fact being connected to form together a single component, the peripheral part 16 forming a collar with respect to the end surface 13.
Thus, in the absence of stress, the one-piece interface 5 takes for example the form of a disk of material of small thickness compared with its transverse dimension (that is to say its diameter).
When the interface 5 and the buffer 6 are both one-piece components, they have comparable transverse dimensions. In particular, when they each take the form of a disk of material, for convenience of manufacture they will preferably be chosen of the same diameter. However, it is equally possible to use a buffer having a diameter different from that of the interface, in particular a greater diameter in order to attenuate the edge effects of the tool on the worked surface.
Moreover, for reasons which will become apparent hereinafter, a deformable ring 17 is provided interposed between the peripheral part 16 of the interface 5 and the return means 15.
In practice, that ring 17 is fastened to the peripheral part 16 on the other side thereof to the buffer 6, i.e. on the same side as the support 4, so that the latter is surrounded by the ring 17.
The ring 17 is preferably of circular longitudinal section, but could equally be of a section of more complex shape, in particular oblong, polygonal, rectangular or square. Moreover, it is placed on the peripheral part 16 concentrically with the support 4.
The return means 15 are described next.
They comprise at least one elastically flexible strip 18 which projects transversely from the support 4, is connected rigidly to the support 4 at a first end 18a, and is connected to the peripheral part 14 of the buffer 6 by a second end 18b, referred to as free end, which is an opposite end to the first end 18a. 
In this way, under the effect of a force exerted longitudinally on the peripheral part 14 opposite that strip 18, the latter deforms while exerting on the peripheral part 14 an opposite reaction to said force.
In practice, the return means 15 comprise a plurality of such strips 18, distributed uniformly around the periphery of the support 4, to act on the whole of the peripheral part 14 of the buffer 6.
The return means 15 in fact take the form of a star-shaped part 19 rigidly fastened to the support 4.
This star-shaped component 19 has a central part 20 from which project a plurality of branches 18 each forming an elastically flexible strip extending radially in a transverse plane.
To fasten the star-shaped component 19 to the support 4, its central part 20 is, in practice, clamped between the jaws 7, 8 of the support 4, its centering being provided by means of a hole 21 through its center through which the pin 9 on the top jaw 8 passes, the assembly being held by fastening means such as screws which, passing through the top jaw 8 and the central part 20 of the star-shaped component 19, engage in the lower jaw 7.
When, in a previously described embodiment, the one-piece buffer 6 comprises a plurality of petals 14b, the same number of branches 18 are provided on the star-shaped component 19 as there are petals 14b, the star-shaped component 19 being oriented so that each branch 18 is in line with a petal 14b. Accordingly, if the buffer 6 comprises seven petals 14b, the star-shaped component 19 comprises seven branches 18, each able to provide the elastic return for one petal 14b. 
The ring 17 is fastened to the interface 5, it being possible for this fastening to be provided by any means, bonding being however preferred, in particular on account of its simplicity.
In the embodiment represented, the diameters of the interface 5, of the buffer 6 and of the star-shaped component 19 are at least twice that of the diameter of the support 4.
Moreover, in the case of surfacing an ophthalmic lens, the diameters of the interface 5 and the buffer 6 are chosen to be substantially equal to the diameter of the lens 3, so that the diameter of the support 4 is considerably less than the diameter of the lens 3.
The use of the tool 1 is illustrated in FIGS. 2 and 3.
In this case this is for surfacing or grinding an aspheric convex face 2 of an ophthalmic lens.
The lens 3 is mounted on a rotary support (not shown) by means of which it is rotationally driven about a fixed axis Y.
The tool 1 is applied against the face 2 with a sufficient force for the buffer 6 to conform to its shape. Here the tool 1 is free to rotate while nevertheless being off-center compared to the optical surface 2. Forced rotational driving of the tool, by means provided for that purpose, may however be provided.
The relative rubbing between the optical surface 2 and the buffer 6 is sufficient to rotationally drive the tool 1 in the same direction as that of the lens 3, about an axis substantially coincident with the axis X of symmetry of the support 4.
The optical surface 2 is irrigated with an irrigation fluid which is abrasive or non-abrasive depending upon whether or not the buffer itself has that function.
To sweep the whole of the optical surface 2, the tool 1 is moved during surfacing along a radial trajectory, the point of intersection of the rotational axis X of the tool 1 with the optical surface 2 moving to and fro between two turn-back points, namely an outer turn-back point A and an inner turn-back point B, both these points being at a distance from the rotational axis Y of the lens 3.
Thanks to the compressibility of the central part 5a of the interface 5, the central part 6a of the buffer 6 deforms to conform to the shape of the optical surface 2.
Thanks to deformation of the flexible strips 18, the peripheral part 14 of the buffer 6 deforms to conform to the shape of the optical surface 2.
Given the rigidity of the support 4, material is mostly removed in line with the end surface 13, i.e. material is essentially removed by the central part 6a of the buffer 6.
The peripheral parts 14 of the buffer 6 and 16 of the interface 5 have an essentially stabilizing role, thanks to the increased lift or seating of the tool 1 relative to a conventional tool whose buffer and interface would be limited to the central parts 5a, 6a, and also thanks to the return means 15, which maintain permanent contact between the peripheral part 14 of the buffer 6 and the optical surface 2.
The deformable ring 17 enables smoothing of the stress distribution exerted on the peripheral rim of the interface 5 and thus on the buffer 6 by the strips 18.
It follows that, regardless of the location of the tool 1 on the optical surface 2, and regardless of its rotational speed, its rotational axis X is always colinear or substantially colinear with the normal n to the optical surface 2, so that the orientation of the tool 1 is optimized at all times.
In the embodiment illustrated in FIGS. 1 and 2, the end surface 13 of the support 4 is plane.
The tool is thus adapted for surfacing a certain range of optical surfaces 2 with different curvatures.
To modify the adaptability of the tool 1, it is possible to bias the return means 15 by twisting the flexible strips 18 so that they are already flexed at rest, in one direction or the other.
If at rest the strips 18 are straight or flexed away from the end surface 13, the tool 1 is intended for concave optical surfaces 2, whereas if at rest the strips 18 are bent toward the end surface 13, the tool 1 is intended for convex optical surfaces 2.
In a first variant which is not illustrated, the end surface 13 of the support 4 is convex, the tool 1 thus being intended for optical surfaces 2 having a more pronounced concavity.
In a second variant which is not illustrated, the end surface 13 of the support 4 is on the contrary concave, the tool 1 thus being intended for optical surfaces 2 having a more pronounced convexity.
Of course, it is possible to combine the concave or convex embodiment of the end surface 13 with biasing of the return means 15, as described above.
French patent application 2 857 610, to which corresponds U.S. patent application 2006/0154581, proposes that the elastic retain means, rather than being in the form of a star-shaped component such as component 19 illustrated in FIGS. 1 and 2, should have a continuous peripheral part bearingly cooperating with the peripheral part of the buffer such as buffer 6, directly or via only the interface such as interface 5 (no deformable ring such as 17 being provided), the elastic return means comprising, in addition to the continuous peripheral part, a flat or curved collar rigidly fastened, inside, to the support such as support 4, that collar being formed by a pierced or unpierced wall.
The continuous character of the peripheral part of this return means makes it possible to increase the evenness of the surfacing performed by the tool.
French patent application 900 356, to which corresponds U.S. patent application 2008/0171502, proposes that the rigid support should belong to a base comprising a flexible collar surrounding the rigid support with the elastically compressible interface covering an end surface of the collar situated on the same side as the end surface of the rigid support.
By virtue of the collar, the contact area between the interface and the rest of the tool is particularly large, which ensures a uniform distribution of the pressure applied on the surface to work and thereby makes it possible to perform surfacing steps giving a high quality finish.